The events of Sep. 11, 2001 instigated an urgency for more effective and stringent screening of airport baggage. The urgency for security expanded from an inspection of carry-on bags for knives and guns to a complete inspection of checked bags for a range of objects and/or materials with particular emphasis upon concealed explosives. X-ray diffraction imaging (XDI) is a technology currently employed for screening. In XDI, an X-ray source sends an X-ray beam via a primary collimator towards one or more potential threat materials, which are identified by means of their X-ray diffraction (XRD) profile, and a transmission detector detects an undeflected portion of the X-ray beam to determine an attenuation of the undeflected portion.
The X-ray source includes an anode and a cathode that generates an electron beam. As the anode is heated by the electron beam, the anode expands and a focus of the X-ray source may move outside an acceptance window of the primary collimator. An acceptance window of the primary collimator is a window inside of which the primary collimator transmits a portion of X-rays incident on the primary collimator. The movement of the focus deteriorates an amount of X-rays that pass through the primary collimator and reduces a number of photons that are detected by the detector. The reduction in the number of photons detected by the detector leads to a lower number of photons represented by an XRD profile, poor detection, and increase in the false alarm rate of the detection of the treat materials, such as a plastic explosive.